1. Field of Invention
This invention relates to an ultrathin steel foil which is suited for use as an electromagnetic shielding material and which has excellent shielding characteristics to electromagnetic waves.
2. Description of Prior Art
Steel foils have been used in computers, etc, for avoiding erroneous operation due to external magnetic waves, for protecting electromagnetic recording data, and as various kinds of shielding materials for protecting against sources of electromagnetic waves.
There are known electromagnetic shielding materials which are coated with conductive paints on plastic base sheets, and such materials which are mixed with metallic powders or chips into the plastic materials.
However, the former is difficult to process into a base sheet. The base sheet is low in shielding effect because it has not electromagnetic wave shielding characteristics, and the conductive paint involves high cost. On the other hand, the latter also presents difficulties. For example, since the metallic powders or chips are mixed into the plastic materials, the powders or chips are exposed at the surfaces of the resulting products. Also, anti-shock properties are deteriorated. In addition, it is necessary to mix large amounts of metallic powders or chips to provide uniform shielding effect, thus resulting in high cost.
In view of the foregoing circumstances, there is a need for shielding materials which are lower in cost than conventional materials, have uniform shielding effect, and may be easily applied to various parts of machinery, etc.